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Pension and Other Postretirement Benefits (Details 12) - Other postretirement benefit plans [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
Ultimate health care cost trend rate 4.50%  
Health care cost trend rate assumed 6.86% 6.44%
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]    
One Percentage Point Increase, Effect on postretirement benefit oblilgation $ 261  
One Percentage Point Decrease, Effect on postretirement benefit oblilgation (242)  
One Percentage Point Increase, Effect on postretirement benefit cost 11  
One Percentage Point Decrease, Effect on postretirement benefit cost $ (10)